1. Technical Field
The present invention relates to a method of moving an optical pickup, the optical pickup, and an optical disc apparatus capable of being applied to a case in which an aberration correction mechanism is composed of, for example, a liquid crystal. The present invention can simplify and miniaturize the optical pickup and further can prevent the deterioration of various characteristics even if the aberration correction mechanism is composed of the liquid crystal and the like by transmitting a drive signal of an actuator and a drive signal of an aberration correction mechanism by multiplexing them.
2. Background Art
Conventionally, in an optical pickup of an optical disc apparatus, it is required to reduce the size and the weight of an actuator for moving an objective lens as the transmission rate and the density of an optical disc is increased.
Further, since the optical pickup is required to accurately reproduce data from bit trains created in a high density, it is proposed to dispose an aberration correction mechanism for correcting the aberration of a laser beam.
That is, when the numerical aperture of the objective lens is increased by an increase in the density of the optical disc, it is difficult for the optical pickup to create a beam spot having a predetermined shape on the information recording surface of the optical disc due to aberration caused by the dispersed thickness of the optical disc. As a result, crosstalk is increased and a C/N ratio is deteriorated in a reproduced signal that is the result of received return light, thereby an error rate is deteriorated in the optical disc apparatus.
Japanese Unexamined Patent Application Publication No. 2000-131603 proposes an arrangement for correcting the wavefront of a laser beam by a lens interposed between an objective lens and a laser beam source as an aberration correction mechanism for correcting the aberration.
Incidentally, it may be difficult for this type of the aberration correction mechanism to sufficiently correct the aberration because positional dislocation is arisen between the aberration correction mechanism and the objective lens. Thus, it is contemplated to hold the objective lens and the aberration correction mechanism integrally.
In this case, however, since the objective lens and the aberration correction mechanism are moved integrally by an actuator, the weight of the subject to be moved by the actuator is increased. Thus, it is difficult to reduce the size and weight of the optical pickup. In particular, when an optical disc having a multi-layered information recording surface is accessed, it is difficult to reduce the size of the optical pickup because the movable range of the aberration correction mechanism increases.
Thus, it is contemplated to compose the aberration correction mechanism of a liquid crystal in place of the aberration correction mechanism composed of the lens. That is, when the aberration correction mechanism is composed of the liquid crystal, even if the liquid crystal is moved by an actuator together with an objective lens, it is contemplated that the weight of a subject to be moved can be reduced as compared with the case in the aberration correction mechanism is composed of the lens. Thus, this arrangement seems to be suitable to the reduction of size and weight of the optical pickup.
However, when the aberration correction mechanism is composed of the liquid crystal, a drive signal must be supplied to the liquid crystal, from which a problem is arisen in that the arrangement of an optical pickup is made complex by a line for supplying the signal. That is, in the actuator of the conventional arrangement, a tracking control voice coil (tracking coil) and a focus control voice coil (focus coil) are disposed on the objective lens side as well as a magnetic circuit holding these two types of the voice coils on a securing side is disposed, and tracking control and focus control are executed by moving these two types of the voice coils according to a tracking error signal and a focus error signal. Thus, when a liquid crystal drive signal supply line is provided additionally, it cannot be avoided that the arrangement of the optical pickup is made complex thereby.
Further, the provision of the liquid crystal drive signal supply line makes it difficult to drive the actuator at a high speed. Further, when the signal supply line is simply composed of a cable, the tension of the cable is changed when it is moved, and there is a possibility that the objective lens is not smoothly moved.
Incidentally, in a current optical pickup, the movable side thereof is held by suspensions composed of slender rod-shaped springs, and signal supply-lines for the two types of the voice coils are composed of the suspensions. Thus, there is contemplated a method of increasing the number of the suspensions to transmit the liquid crystal drive signal. With this arrangement, however, the weight of a movable section is increased and further the spring constants of the suspensions are increased, whereby it is difficult to drive the actuator at a high speed. Further, it is difficult to reduce the size of the optical pickup. Furthermore, it is also difficult to keep the balance of the spring constants of the respective suspensions.